Optical properties of the crescent-shaped nanohole antenna.

We present the first optical study of large-area random arrays of crescent-shaped nanoholes. The crescent-shaped nanohole antennae, fabricated using wafer-scale nanosphere lithography, provide a complement to crescent-shaped nanostructures, called nanocrescents, which have been established as powerful plasmonic biosensors. With both systematic experimental and computational analysis, we characterize the optical properties of crescent-shaped nanohole antennae and demonstrate tunability of their optical response by varying all key geometric parameters. Crescent-shaped nanoholes have reproducible sub-10-nm tips and are sharper than corresponding nanocrescents, resulting in higher local field enhancement, which is predicted to be |E|/|E(0)| = 1500. In addition, the crescent-shaped nanohole hole-based geometry offers increased integratability and the potential to nanoconfine analyte in "hot-spot" regions, increasing biomolecular sensitivity and allowing localized nanoscale optical control of biological functions.